Allocate more video memory? Is there anyway to force this

TL;DR: How to get more gpu memory, need an indication at how much we use before busting and if unity can't help with 1 at least have something to support multi scenes setup.

So I work my environements like a good environement artist that I am (some gigantic house), then bake and at some point I get this error:
OpenCL Error. Falling back to CPU lightmapper. Error callback from context: Max allocation size supported by this device is 1.50 GB. 2.58 GB requested.

Unity then revert back to progressive cpu wich is terrible because it take like 10 hours instead of 20 minutes.
Of course the classic way to fix is reduce your sample, reduce the light map size...

Then you reach the point where you don't want your lighting to looks like total garbage so you can close the Game and editor view windows and even reduce Texture quality (project setting/quality)
yes it help and no, it do not reduce the lightmap quality (just don't forget to change it back to full res afterward)

BUT THEN... you reach a point that this is not enough so... time to split the scene in two scenes (with all the problems that go with it). Then three scenes, then four...

I have a RTX2060 with like 6 GB GDDR6 memory, I'm not sure why I only get 1.50 GB supported, I guess it's a driver related thing.

Anyway these are the crucial questions:

1- Is there any way to allocate moar memory? In unity or windows, if not, can Unity do anything about it?

2- Is there any indication of how much memory you are currently using, instead of just displaying it when you bust? (Press Generate Lightmap get a message "you are at 1.25GB Max allocation size supported by this device is 1.50 GB, 0.25GB until apocalypse...
if not, can Unity do anything about it?

3- Any tool that would support multi scenes setup would be great. My current workflow go like this I have 5 scenes:
Scene 1: Anything character related, and non art related stuff
Secne 2: Outside environement stuff
Scene 3: Inside environement A
Scene 4: Inside environement B
Scene 5: Inside environement C

Then I bake Outside alone, then same with Inside Environnements but of course I need a some sort of mesh shell to occlude lights from goint trough the backface of the inside walls, but I need to hide it in play mode, that and the VolumeProfile and directionnal temporary used... then I need to load each scene and bake each reflection probes then I shot myself in the head because I need to do it again with each scene set as active because Light prbes need to be splitted in each scenes because you can't just put everything lightmap static, you need to use the lightprobe system or else you will bust you memory before reaching this point thus having 8 scenes instead of 5... so yeah


So is there a magic tool that I missed? if not, can Unity do anything about it?

Sorry for the wall of text and my terrible engrish but I think I'm asking good questions here please don't let this post die.

 

My Nvidia 3070 Ti is able to address 8GB VRAM, it is possible to use my Intel UHD? Intel should be able to address shared 15,9GB. And it is possible use this shared VRAM by Nvidia?